Generally, fine pattern formation is carried out by the photolithography in manufacturing processes of a semiconductor device. A number of transfer masks called photomasks are usually used for this fine pattern formation. The transfer mask includes generally a transparent glass substrate having thereon a fine pattern made of a metal thin film or the like. The photolithography is used also in the manufacture of the transfer mask.
As a type of transfer mask, a phase shift mask is known apart from a conventional binary mask having a light-shielding film pattern made of a chromium-based material on a transparent substrate. This phase shift mask is of a structure having a phase shift film on a transparent substrate. This phase shift film is configured to provide a predetermined phase difference and is made of, for example, a material containing a molybdenum silicide compound or the like. Further, use has also been made of a binary mask using, as a light-shielding film, a material containing a metal silicide compound such as a molybdenum silicide compound.
In recent years, with higher integration of semiconductor devices, patterns finer than the transfer limit of the photolithography using the conventional ultraviolet light have been required in the semiconductor industry. In order to enable the formation of such fine patterns, the EUV lithography being an exposure technique using extreme ultraviolet (Extreme Ultra Violet: hereinafter referred to as “EUV”) light is expected to be promising. Herein, the EUV light represents light in a wavelength band of the soft X-ray region or the vacuum ultraviolet region and, specifically, light having a wavelength of about 0.2 to 100 nm. A reflective mask has been proposed as a mask for use in the EUV lithography. In the reflective mask, a multilayer reflective film configured to reflect exposure light is formed on a substrate and an absorber film configured to absorb exposure light is formed in a pattern on the multilayer reflective film.
The photolithography is used also in the manufacture of the reflective mask. For example, Patent Document 1 discloses a typical structure of a reflective mask blank for use in the manufacture of a reflective mask.